Patients with pancreatic endocrine tumors that synthesize both insulin and islet amyloid polypeptide (IAPP) have higher circulating IAPP concentrations than those that synthesize insulin only. The relationship between the IAPP and insulin concentrations following glucagon injection is concordant in patients with tumors that express both insulin and IAPP. The relationship between the IAPP and insulin concentration following glucagon injection is discordant in patients with insulinomas that do not express IAPP. This study was designed to determine if a newly recognized protein, IAPP, is present in insulin secreting tumors of the pancreas and, if so, whether this protein is present in high concentration in the blood (like insulin). A newly developed technique for measurements of insulin will also be assessed. Preliminary assessments suggest that diagnostic cutoff between relative hyperinsulinemia during hypoglycemia is a threshold of 3 mu/nl, with normals being lower and insulins being higher. The study was inactivated in September 1998, since the insulin assay under study became a routine test in the Mayo laboratory.